1. Field of the Invention
The present invention relates to a trunnion-mounted ball valve and more particularly to a trunnion-mounted ball valve which has a pair of self-centering, floating metal seals.
2. Description of the Prior Art
U.S. Pat. No. 3,269,692, entitled Ball Valve Construction, issued to Homer J. Shafer on Aug. 30, 1966 teaches an improvement for use in a trunnion-mounted ball valve having a housing forming a cavity laterally around the ball and flow tubes longitudinally of the valve, seating rings adjustable longitudinally between the ball and the flow tubes, and resilient seals between the seating rings and the ball. The improvement includes a device for utilizing the cavity pressure to force the seating ring on the downstream side of the ball to seal against the ball radially outwardly of the resilient seal. The device is a seating ring construction having a greater area exposed to cavity pressure acting toward the ball than its area exposed to cavity pressure acting away from the ball.
U.S. Pat. No. 3,269,691, entitled Ball Valve Seal Support, issued to Robert J. Meima and James D. Aiken on Aug. 30, 1966 teaches an improvement for a valve which includes a casing having a central bore terminating in shoulders defining axially outer reduced bores which terminate in shoulders defining inlet and outlet ports communicating with the bores; a ball including a flow passage rotatably mounted in the central bore and valve seats slidably and rotatably mounted in the reduced bores and having enlarged portions terminating in shoulders. The valve also includes a ball engaging valve seal slidably mounted on each of the portions. The valve seats and the portions containing the seals are movable from an operative ball engaging position to a ball clearance position against the bore and port defining shoulders. There is a cam slot formed in the outer periphery of the seats. There are pins fixed to the casing and projecting into the slots to effect axial movement of the seats between the positions upon rotation of the seats. A spring acts between the enlarged portion shoulders and the seals to urge the seals against the ball in operative position. The valve casing includes a removable cover for the insertion of the ball, a recess formed in the outer peripheries of the valve seats, and retaining pins projecting from the cover and into the recesses to limit the movement of the valve seats toward the ball to limit the pressure of the seals against the ball and retain the valve seats in operative position.
U.S. Pat. No. 3,226,080, entitled Ball Valve Seat, issued to William E. Lowry on Dec. 28, 1965, teaches a rotatable plug valve that includes a valve body that has a bore extending therethrough, a spherical valve member that is positioned in the bore and that has a port the axis of which is alignable with the axis of the bore in the open position of the valve and an aperture in the valve body. The rotatable plug valve also includes a stem that has an inner end which is engaged with the valve member and an axially outer end which extends through the aperture in the valve body and a device for forming a seal between the aperture and the stem. The rotatable plug valve further includes detachably connected end members which extend into each end of the bore in the valve body with each end member having a device which limits entry of the end member into the valve body a predetermined amount and with each end member also having a passage with which the port in the valve member can be aligned to form the run of the valve and an axially inner end having a portion taperingly diverging axially outward from the passage. The rotatable plug valve still further includes an annular groove in the taperingly diverging portion of the axial inner end with each annular groove having an inner and outer cylindrical walls which are disposed in coaxial relation with the respective passage and also having an end wall which is disposed in substantially normal relation with the cylindrical walls. There is also an annular seat member of deformable material which is positioned in each of the grooves with each seat member being of lesser radial thickness than the radial thickness of its groove so that in the uncompressed condition there is substantial clearance between the seat member and groove along the entire length of both the inner and outer circumferences of the groove. Each seat member has a portion which extends beyond the surface of the taperingly diverging portion terminating in a tapered surface to oppose the spherical surface of the valve member with each end member extending into the body bore an amount sufficient to force the seat member into intimate sealing contact with the spherical surface of the valve member upon assembly thereby deforming the seat member a limited amount so that the seat members do not completely fill the groove either during assembly or operation within rated pressure whereby the seat members act as a columnar spring against the spherical valve member.
Other ball valves are taught in U.S. Pat. No. 3,269,693, entitled Ball Valve Seat, issued to Ronald A. Gullick on Aug. 30, 1966, and U.S. Pat. No. 3,357,679, entitled Multi-Material Elastomer Seal, issued to Robert A. Gullick on Dec. 12, 1967.
In all of the trunnion-mounted ball valves of the prior art the sealing rings are separated from the ball by a resilient, deformable seal in order to correct for any misalignment of the sealing ring and the ball. If there is not a resilient, deformable ring placed between the sealing ring and the ball, the ball valve will not seal properly. However, scale becomes deposited on the surface of the ball and acts as an abrasive thereby filing down the surface of the resilient deformable seal to a point where it can no longer seal the ball valve. At that time the ball valve must either be replaced or repaired.
The inventor has considered eliminating the resilient, deformable seal between the sealing ring and the ball. The difficulty with eliminating the resilient, deformable seal is that the ball valve will leak unless the sealing ring is in perfect contact with the ball. It is impossible to realize perfect contact between the ball and the sealing rings as long as the sealing ring can only move along the axis of the bore of the valve body.